Properties Of Aqueous Solutions Research Articles

Antibodies Processed Using High Dilution Technology Distantly Change Structural Properties of IFNγ Aqueous Solution.

Terahertz spectroscopy allows for the analysis of vibrations corresponding to the large-scale structural movements and collective dynamics of hydrogen-bonded water molecules. Previously, differences had been detected in the emission spectra of interferon-gamma (IFNγ) solutions surrounded by extremely diluted solutions of either IFNγ or antibodies to IFNγ without direct contact compared to a control. Here we aimed to analyse the structural properties of water in a sample of an aqueous solution of IFNγ via terahertz time-domain spectroscopy (THz-TDS). Tubes with the IFNγ solution were immersed in fluidised lactose saturated with test samples (dilutions of antibodies to IFNγ or control) and incubated at 37 °C for 1, 1.5–2, 2.5–3, or 3.5–4 h. Fluidised lactose was chosen since it is an excipient in the manufacture of drugs based on diluted antibodies to IFNγ. After incubation, spectra were recorded within a wavenumber range of 10 to 110 cm−1 with a resolution of 4 cm−1. Lactose saturated with dilutions of antibodies to IFNγ (incubated for more than 2.5 h) changed the structural properties of an IFNγ aqueous solution without direct contact compared to the control. Terahertz spectra revealed stronger intermolecular hydrogen bonds and an increase in the relaxation time of free and weakly bound water molecules. The methodology developed on the basis of THz-TDS could potentially be applied to quality control of pharmaceuticals based on extremely diluted antibodies.

Raman spectroscopy study for the systems (LiCl-H2O and LiCl-MgCl2-H2O): Excess spectra and hydration shell spectra

The micro-structure of hydration shell of solute in water is significant for understanding the properties of aqueous solutions. Raman spectroscopy has been employed for studying the hydration shell structure of the solute for decades, however, Raman imaging data is still seriously overlapped, making it challenging to obtain information on the spectrum of hydrated water molecules. In this paper, Raman spectroscopy was employed to study the O-H vibration peaks of LiCl aqueous solution and LiCl-MgCl2-H2O mixed aqueous solution. The changes of stretching vibration peak of 2800 ∼ 3800 cm-1O-H and hydrogen bond network structure in aqueous solution were analyzed at room temperature and ion association. With the increase of magnesium salt ratio, the damage of solute to the bulk water gradually decreases in the mixed solution, which indicated that LiCl has a more significant influence on the bulk water molecules. It is mainly due to the intense hydration of Li+, which can not only affect the water molecules in the first hydration shell but also affect the water molecules in the second hydration shell. The number of water molecules in the first hydration shell were obtained by extracting the spectra of different solute first hydration shells from the solution spectra. Those spectra of the hydration shell were employed to study the micro-structures of the first hydration shells of anions, and the aggregation behavior of ions in the the mixed solution.

AQUEOUS SOLUTIONS OF CHITOSAN: VISCOMETRIC AND FLOCCULATION PROPERTIES

The hydrodynamic and flocculation properties of aqueous solution of chitosan (CS) were investigated at room temperature. The viscometric data of dilute CS solutions were discussed in terms of Wolf method as a function of polymer concentration, salt nature (NaCl, NaNO3, and CaCl2) and concentration. The flocculation properties in emulsions of some commercial pyrethroid insecticides (Fastac 10 EC (F), Decis (Dc) and Karate Zeon (KZ)) were evaluated. The viscosity measurements reveal that the experimental data fit well with the Wolf model and the [η] values decrease in salt aqueous solutions. For the same insecticide concentration (0.02%, v/v), UV-Vis spectroscopy measurements show maximum removal efficiency around 90% for Fastac 10EC and Decis and 80% for Karate Zeon. The residual KZ absorbance decreased with the increase of insecticide concentration in the initial emulsion, from 80% for the lowest concentration (0.02%, v/v) to around 90% for the highest one (0.06%, v/v). The supernatant zeta potential dependence on the chitosan dose pleads for the charge neutralization as the main mechanism for the flocculation of pyrethroid insecticide particles.

Hydrogen bonding and surface tension properties of aqueous solutions of tetrahydrofuran

Significant changes observed in the tetrahydrofuran—water mixtures of different molar ratios have been determined the extent of intermolecular association via quantitative Raman experiment. The hydrogen bonding changes with the addition of tetrahydrofuran. The changes of surface tension are analyzed with hydrogen bonding in the mixtures. The result shows that the strengthening of hydrogen bonding between tetrahydrofuran and water contributes to weak the surface tension in the solutions. The correlation between surface tension and mole fractions of tetrahydrofuran is non-linear. This study provides an experimental basis for enriching the hydrogen bonding theory of multivariate aqueous solution systems.

Very low surface tensions with “Hedgehog” surfactants

Previous studies [Langmuir, 2014, 30, 21, 6057–6063, Phys. Chem. Chem. Phys., 2017,19, 23869–23877] have shown that surfactants bearing highly-methylated alkyl tails (so-called “hedgehog” groups) are able to reduce the limiting surface tension at the aqueous critical micelle concentration (CMC) to γCMC ~24 mN m−1, which is considerably lower than for common n-alkyl tail surfactants (30–40 mN m−1). In the quest to develop even more effective and efficient non-fluorinated surfactants, this study introduces new amphiphiles having double and triple hedgehog tails and examines relationships between surfactant structure and aqueous solution properties. Of particular interest are links between γCMC, the effective hydrophobic-tail layer density (ρlayer) and total number of carbon and silicon atoms in the hydrophobic tails (NC+Si). Interestingly, γCMC is seen to depend on ρlayer rather than NC+Si, and ρlayer ~0.63 g cm−3 appears to be an optimal surface layer density for promoting low γCMC. For a surfactant bearing trimethysilyl (TMS) chain tips, exchanging the surfactant counterions from Na+ to Mg2+ reduced γCMC from 23.8 mN m−1 to 21.5 mN m−1, which is very low for a hydrocarbon surfactant, and comparable to typical fluorinated surfactants. A new measure of the ability of different surfactants to lower surface tension is proposed, which is helpful for targeting low surface energy (tension) non-fluorinated surfactants. In terms of both γCMC and CMC TMS-terminal tips are shown to be key groups for promoting hydrophobicity and/or low surface tensions.

Experimental study on the characteristics of temperature dependent surface/interfacial properties of a non-ionic surfactant aqueous solution at quasi-thermal equilibrium condition

The surface/interfacial properties of liquid at elevated temperatures are fundamental issues for wide applications where the surface force matters. The dynamic characteristics of wetting behavior and surface tension (ST) of surfactant solutions remain unclear at thermal equilibrium, especially at high temperature. Utilizing a quasi-thermal equilibrium setup, the temperature dependence of the surface/interfacial properties of liquids (ultra-pure water and aqueous surfactant solutions) at temperature ranging from 10 to 90 °C (1 atm) are studied, by the sessile drop method and pendant drop method, respectively. A decreasing trend of the initial ST and contact angle (CA) is observed with the increase of temperature. During evaporation, the increase of the local relative humidity around the droplet has a crucial influence on CA. The obtained ST and CA are based on the thermodynamic model with modified coefficients, which can well describe the general trends for different temperatures and concentrations. For the ultra-pure water, the droplets will be pinned suddenly on the heating surface, until a sudden contraction occurs with evaporation. However, the surfactant-laden droplet shows different dynamical behaviors from ultra-pure water. Three different stages, named spreading-controlled Stage I, evaporation-controlled Stage II, and depinning-controlled Stage III are found for the dynamic evolution of surfactant-laden droplet. In what follows, the different droplet behaviors are also analyzed for surfactant solution and ultra-pure water.

Enhancement of the Luminescence Properties of Eu (III) Containing Paramagnetic Saponite Clays

In this study, 1,10-phenanthroline molecules were introduced in the interlayer space of a paramagnetic synthetic saponite clay containing both Eu3+ and Gd3+ ions in structural positions. Two samples with different loading of phenanthroline dye were prepared. The resulting hybrid materials possessed improved optical emission properties due to an efficient antenna effect from the phenanthroline to the Eu3+ centers; this effect was demonstrated to be higher than the metal-to-metal Gd3+-Eu3+ energy transfer previously studied. Insights on the relaxometric properties in aqueous solution of the solids after incorporation of the antenna groups were also obtained through NMR relaxometric analyses.

Thermoresponsive Polymers Based on Tertiary Amine Moieties.

Thermoresponsive polymers exhibiting unique reversible phase transition properties in aqueous solution in response to temperature stimuli have been extensively investigated. In the past two decades, thermoresponsive polymers based on tertiary amine moieties have achieved considerable progress and become an important family of thermoresponsive polymers, including tertiary amine functionalized poly((meth)acrylamide)s, poly((meth)acrylate)s, poly(styrene)s, poly(vinyl alcohol)s, and poly(ethylene oxide)s, which exhibit lower critical solution temperature and/or upper critical solution temperature in water or aliphatic alcohols. Their phase transition behavior can be modulated by the solution pH and CO2 due to the protonation of tertiary amine moieties in acidic condition and deprotonation in alkaline condition and the charged ammonium bicarbonate formed by the tertiary amine moieties and CO2 . The aim of this review is to summarize the recent progress in the thermoresponsive polymers based on tertiary amine moieties.

Volumetric, compressibility and viscometric properties of diphenhydramine hydrochloride in aqueous solutions of electrolytes: An insight into interactional characteristics

The density (ρ), speeds of sound (u), and viscosity (η) measurements for diphenhydramine hydrochloride (anti histaminic drug) in aqueous solutions of different electrolytes (NaCl, KCl, RbCl, MgCl2, CaCl2 and SrCl2) have been carried out. Volumetric and compressibility properties of aqueous drug solution containing electrolyte have been explained on the basis of trends observed in different enumerated parameters and information regarding various solute–solvent interactions prevailing in the ternary system have been accessed. The effect of drug concentration and temperature on the interactional behaviour of the considered system has been analyzed by carrying out the experiments at different drug content (0.03–0.17 mmol.kg−1) and temperatures (298.15–313.15) K at definite interval of 5 K. The participation of specific as well as non-specific interactions between diphenhydramine hydrochloride (DPH) and electrolytes in aqueous solution has been found to play its role in stabilization of solution mixture. Further, the structural changes induced by drug molecules in solution containing different electrolytes with same concentration have been illustrated with the help of viscosity studies. The results obtained from different employed studies have been used to elucidate solute/solvent–solvent/solute interactions in aqueous electrolytic solution. As electrolytes are integral part of biological system, hence, the study of such systems may be very useful in understanding the mechanism of drug action that ultimately facilitates the illustration of drug – electrolyte chemistry.

Photofluorochromic water-dispersible nanoparticles for single-photon-absorption upconversion cell imaging

Photofluorochromic diarylethene (DAE) molecules have been widely investigated due to their excellent fatigue resistance and thermal stability. However, the poor water solubility of DAEs limits their biological applications to some extent. Herein, we reported two kinds of water-dispersible DAE nanoparticles (DAEI-NPs and DAEB-NPs), in which DAE molecules were stabilized by the amphiphilic polymer DSPE-mPEG2000 using the nanoprecipitation approach. The fabricated nanoparticles retain well-controlled luminescence and fluorescence photoswitching properties in aqueous solution, which could be reversibly switched on and off under the alternating irradiation of ultraviolet (UV) and visible light. In addition, the closed-ring isomers of DAEB-NPs performed hot-band-absorption-based photon upconversion when excited by a 593.5 nm laser. Bearing excellent photophysical properties and low cytotoxicity, DAEB-NPs were applicable for upconversion cell imaging without high-excitation power density and free from oxygen removal. Additionally, the imaging process could be switched on by regulating the photofluorochromic nanoparticles.

Design and synthesis of curcumin nanostructures: Evaluation of solubility, stability, antibacterial and antioxidant activities

By coupling a quaternary pyridinium compound and curcumin (CM), a new antimicrobial agent called CP was obtained. The poor water-solubility was the most important limiting factor in the use of CM and CP. To address this problem, a hydrophilic hyperbranched polyglycerol (PG) was synthesized and reacted with CM and CP via Schiff base reaction to form two new macromolecules. Due to the presence of polymer, the solubility and stability of CM and CP increased significantly in aqueous media. Since the new macromolecules were including the hydrophilic polymeric and curcumin hydrophobic units, they self-assembled into spherical nanostructures, which were characterized by Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images. The synthetic nanostructures exhibited a controlled release of curcumin unit in the acidic environment. In vitro experiments showed that the new macromolecules are potent antibacterial and antioxidant agents.

Thermal Properties of the H2O–CO2–Na2CO3/CH3OH/NH3 Systems at Low Temperatures and Pressures up to 50 MPa

Experimental data on the thermal properties of aqueous solutions at low temperatures and high pressures are necessary to perform an accurate geochemical modeling of ocean worlds, that is, those planetary bodies that can sustain significant reservoirs of the interior liquid for long time periods. We used differential scanning calorimetry (DSC) to determine the values of specific heat capacity and enthalpy of dissociation of CO2-clathrates in the presence of sodium carbonate, ammonia, and methanol at temperatures ≥233 K and pressures ≤50 MPa. We monitored the physicochemical evolution of the systems along the pressure–temperature paths through Raman spectroscopy. The protocol used to form the CO2-clathrates influenced the thermal behavior of the system. Partial recrystallization events from ice to CO2-clathrate during slow heating resulted in out-of-equilibrium heat capacities (Cp) of < 1 J g–1 K–1. After complete melting of the solids, the final aqueous solutions had Cp 2–3 J g–1 K–1. Final fluids richer in dissolved CO2 had a lower Cp. The addition of carbonates and methanol led to a decrease in the melting temperature of both ice and clathrates. Ammonia reacted with CO2 to rapidly form ammonium bicarbonate; however, ice and CO2-clathrates could also stabilize in parallel. In all the studied systems, the formation of clathrates from aqueous solutions without the application of clathrate stabilizers, mechanical agitation, or synthesis from crushed ice led to a low guest occupancy, forming less-stable clathrates with low enthalpies of dissociation (130–275 J g–1). These results have important planetary implications related to the thermal behavior of bodies rich in the compounds of the systems studied, as can be the case of Enceladus. In this research, we show that the level of cage occupancy in clathrates plays a key role in their thermal behavior. Highly occupied clathrates will be robust and will contribute to the retention of heat inside the planetary bodies due to their characteristic low thermal conductivity. However, poorly occupied clathrates will dissociate more easily than water ice, allowing greater heat fluxes through the icy crust and favoring the dissipation of heat to the exterior.

Foaming and rheological properties of aqueous solutions: an interfacial study

Abstract Although aqueous foam is composed of simple fluids, air and water, it shows a complex rheological behavior. It exhibits solid-like behavior at low shear and fluid-like behavior at high shear rate. Therefore, understanding such behavior is important for many industrial applications in foods, pharmaceuticals, and cosmetics. Additionally, air–water interface of bubble surface plays an important role in the stabilizing mechanism of foams. Therefore, the rheological properties associated with the aqueous foam highly depend on its interfacial properties. In this review, a systematic study of aqueous foam are presented primarily from rheology point of view. Firstly, foaming agents, surfactants and particles are described; then foam structure was explained, followed by change in structure under applied shear. Finally, foam rheology was linked to interfacial rheology for the interface containing particles whose surface properties were altered by surfactants.

Low‐Temperature Correlation of Property Data for Dilute Aqueous Lithium Bromide Solution

AbstractA new correlation for some transport properties of aqueous solutions, based on the data published by Sawada et al. [1], is proposed. The main objective of the new fit is to give a smooth transition to the properties of pure water to allow the use of the fit in the region of very dilute solutions. Additionally, the quality of the fit to the experimental data is improved compared to the original correlation. An extrapolation of the new correlation in the other direction, i.e., to higher mass fractions and temperatures, is smooth but does not fully capture the trend described by other experimental datasets. To this end, the correlation has to be refined further.

Molecular Properties and Chemical Transformations Near Interfaces.

The properties of bulk water and aqueous solutions are known to change in the vicinity of an interface and/or in a confined environment, including the thermodynamics of ion selectivity at interfaces, transition states and pathways of chemical reactions, and nucleation events and phase growth. Here we describe joint progress in identifying unifying concepts about how air, liquid, and solid interfaces can alter molecular properties and chemical reactivity compared to bulk water and multicomponent solutions. We also discuss progress made in interfacial chemistry through advancements in new theory, molecular simulation, and experiments.

A mild and straightforward one-pot hyaluronic acid functionalization through termination of poly-(2-alkyl-2-oxazoline)

Hyaluronic acid (HA) of different molar masses from 38 000 to 990 000 g mol−1 were used as terminating agents during the cationic ring-opening polymerisation of 2-methyl-2-oxazoline. HA was first converted into a tetrabutylammonium salt to solubilize it in polar aprotic organic solvents where the termination was conducted by varying the excess of HA units to the growing poly(2-methyl-2-oxazoline) (PMeOx) chains (with various PMeOx degree of polymerisation). This led to HA derivatives with various PMeOx degrees of substitution from 4% up to 13% (determined by 1H NMR). HA-g-PMeOx copolymers were analysed by Size Exclusion Chromatography with on-line detectors (Multi-angle light scattering, Viscometer, Refractive index) in 0.1 mol L−1 LiNO3 to study their macromolecular characteristics in dilute medium. The reaction was applied to functionalize HA with thermo-responsive poly(2-isopropyl-2-oxazoline)-co-poly(2-n-butyl-2-oxazoline) moieties, resulting in materials displaying thermally dependent hydrogel properties in aqueous solutions which could be used for biomedical applications.

Rational Design of Nonbonded Point Charge Models for Divalent Metal Cations with Lennard-Jones 12-6 Potential.

Exploring a metal-involved biochemical process at a molecular level often requires a reliable description of metal properties in aqueous solution by classical nonbonded models. An additional C4 term for considering ion-induced dipole interactions was previously proposed to supplement the widely used Lennard-Jones 12-6 potential (known as the 12-6-4 LJ-type model) with good accuracy. Here, we demonstrate an alternative to modeling divalent metal cations (M2+) with the traditional 12-6 LJ potential by developing nonbonded point charge models for use with 11 water models: TIP3P, SPC/E, SPC/Eb, TIP4P-Ew, TIP4P-D, and TIP4P/2005 and the more recent OPC3, TIP3P-FB, OPC, TIP4P-FB, and a99SB-disp. Our designed models simultaneously reproduce the experimental hydration free energy, ion-oxygen distance, and coordination number in the first hydration shell accurately for most of the metal cations, an accuracy equivalent to that of the complex 12-6-4 LJ-type and double exponential potential models. A systematic comparison with the existing M2+ models is presented as well in terms of effective ion radii, diffusion constants, water exchange rates, and ion-water interactions. Molecular dynamics simulations of metal substitution in Escherichia coli glyoxalase I variants show the great potential of our new models for metalloproteins.

Local structure in lithium chloride solution: a Monte-Carlo simulation study

ABSTRACT Monte-Carlo simulations and the nearest neighbour approach have been employed in the present study to investigate the structural properties of aqueous solutions of LiCl salt at ambient conditions. The calculations are performed at increasing concentration of LiCl starting from c = 0.1 m up to 10 m. The analysis shows that increasing salt concentration results in a reduction of the tetrahedral arrangement of water in favour of a non-tetrahedral arrangement characterised by an O–O–O angle between the reference oxygen and two of its four closest oxygen neighbours at 60°. Moreover, the LiCl concentration has a considerable effect on the hydrogen-bonding structure of water. By correctly choosing the nearest neighbours, it is found that the deviation in water structure is due to the presence of chloride ion, not lithium ion, in the first solvation shell of water. It is also demonstrated that in concentrated LiCl solution Cl− ions can substitute the fourth water neighbour which leads to a tetrahedral network formed by water molecules and Cl− ions around a central water molecule. The analysis of the effect of concentration increase on the arrangement of the four closest water molecules neighbours from a reference lithium cation allows us to elucidate a structural maker role of Lithium ion.

Acid-base equilibria of axial ligand and peripheral pyridyl group with stepwise formation of nine species of aluminum (III) tera(4-pyridyl) porphyrin

As one of the promising molecular catalysts for the two-electron water oxidation initiated through one-electron oxidation of the catalyst, trans-diaqua-coordinated 5, 10, 15, 20-tetra(4-pyridyl)porphyrinatealuminum (III) (AlTPyP(OH2)2) was studied on the protolytic behavior of the axial ligating water molecules and the redox properties in aqueous methanol solution. The reversible stepwise protolytic reactions of the two axially ligated water molecules, as well as four peripheral pyridyl groups at the meso-position of AlTPyP, were characterized using UV–vis absorption spectroscopy, 1H NMR, fluorescence lifetime measurements, and cyclic voltammetry. The result showed that four-step protolytic equilibrium reactions of the axial ligands proceeded under the basic pH condition and those of meso-substituted pyridyl groups did also under the acidic pH condition. All the nine species are in equilibria in the ground states as characterized with each pKa value. On the other hand, they exist as individual species in the excited states having each single exponential decay time constant. Here we will report the first detailed study on the formation of nine species from a single molecule of AlTPyP through protolytic reactions in the pH range between 0.54 and 12.3.

Phase equilibria and thermophysical properties of aqueous solutions of two bis(fluorosulfonyl)imide-based ionic liquids

Ionic liquids comprising bis(fluorosulfonyl)imide (FSI) anion have been recognized to be well suited for technological applications as solvent and electrolyte media. In this work, we thoroughly investigated the thermodynamic and transport behavior of binary aqueous systems of two hydrophobic FSI-based ionic liquids, namely [EMIM][FSI] and [BMPYR][FSI]. Systematic measurements of phase equilibria, density, viscosity, and electric conductivity were conducted, our aim being to provide truly reliable information that would substantially upgrade that existing in the literature. Employing DSC measurements on the neat ILs and dynamic measurements of freezing or cloud point temperatures as well as static solubility measurements for aqueous ILs, phase diagrams for both these systems over a 100 K window were established. Rather large solubilities of water in these ILs allow for measurements of various other properties in the homogeneous IL-rich region. Extensive data thus obtained on water activity in this region were correlated for each system simultaneously with the mutual liquid-liquid solubilities, using an extended SSF (Sum of Symmetrical Functions) equation. This global excess Gibbs energy model not only accurately captures all the VLE, LLE, and SLE data we determined experimentally, but also discloses an enthalpy-driven system energetics with hydrophobic hydration effects that are more pronounced in the case of [BMPYR][FSI]. The measurements of density, viscosity, and conductivity covering the systems from the neat ILs to those almost saturated with water gave positive excess volumes and negative viscosity deviations that rise and diminish, respectively, as T increases. The conductivity increases monotonously with increasing water content and temperature. Accurate functional representations were also established for the volumetric, viscosity, and conductivity data, capturing simultaneously their composition and temperature dependence. The linkage between conductivity and viscosity was further analyzed by means of the fractional Walden rule which provided excellent fits for both isopleths and isotherms and indicated comparatively weaker coupling for the [BMPYR][FSI] system and the direction of the isothermal composition changes. Finally, comparing the FSI ILs with their TFSI analogs, the former were found to be clearly less hydrophobic.